Create a MachineBasicBlock for created IR-level BasicBlock

[paquette]

Summary

While running the lit tests for the most recent version of D45916 (https://reviews.llvm.org/D45916), I found that a couple tests for this pass suddenly started segfaulting. Since the outliner wasn't actually doing anything to the code in either of these tests I got curious.

I found that the pass doesn’t completely create the machine-level constructs necessary to actually add a MachineFunction and MachineBasicBlock to the module. This patch adds in those missing bits. After this, adding the outliner before this pass won’t cause it to segfault.

You can recreate this behaviour by adding the MachineOutliner directly before the pass and having it return false immediately.

[chandlerc]

Good catch, thanks! LGTM

lib/Target/X86/X86RetpolineThunks.cpp

226

using end() would seem a touch more idiomatic to me? Clearly doesn't actually matter much...

[paquette]

Thanks! Switched the begin() to end() as suggested.

Committed in r331307.

lib/Target/X86/X86RetpolineThunks.cpp

void X86RetpolineThunks::createThunkFunction(Module &M, StringRef Name) {
   B.addAttribute(llvm::Attribute::Naked);
   F->addAttributes(llvm::AttributeList::FunctionIndex, B);
 
   // Populate our function a bit so that we can verify.
   BasicBlock *Entry = BasicBlock::Create(Ctx, "entry", F);
   IRBuilder<> Builder(Entry);
 
   Builder.CreateRetVoid();
+
+  // MachineFunctions/MachineBasicBlocks aren't created automatically for the
+  // IR-level constructs we already made. Create them and insert them into the
+  // module.
+  MachineFunction &MF = MMI->getOrCreateMachineFunction(*F);
+  MachineBasicBlock *EntryMBB = MF.CreateMachineBasicBlock(Entry);
+
+  // Insert EntryMBB into MF. It's not in the module until we do this.
+  MF.insert(MF.begin(), EntryMBB);
 }
 
 void X86RetpolineThunks::insertRegReturnAddrClobber(MachineBasicBlock &MBB,
                                                     unsigned Reg) {
   const unsigned MovOpc = Is64Bit ? X86::MOV64mr : X86::MOV32mr;
   const unsigned SPReg = Is64Bit ? X86::RSP : X86::ESP;
   addRegOffset(BuildMI(&MBB, DebugLoc(), TII->get(MovOpc)), SPReg, false, 0)
       .addReg(Reg);